1. Field of the Invention
The invention relates generally to the field of battery chargers, and more specifically to a battery powered controller for a battery powered device.
2. Description of the Prior Art
Numerous types of battery chargers are on the market today which provide the capability of recharging secondary rechargeable batteries, such as nickel-cadmium or other rechargeable batteries. Many of these chargers required the removal of the batteries from the battery powered device to enable recharging. Removal of the batteries was generally negatively viewed, as the battery powered device was out of operation while the batteries were being recharged, unless spare batteries were available. Many other chargers had overcome the aforementioned deficiency by providing the capability to recharge the batteries in situ, while the battery remained affixed to, or within the battery powered device. In this manner, the functionality of the device was maintained while the batteries were being recharged. While the functionality of the devices was maintained, the devices were unavailable for operation in the manner intended, that of being transportable. Also, many of the chargers were "trickle" chargers, chargers which recharged the battery at a very low charging rate, consequently the battery powered device was also unusable for normal operation for extended periods of time, such as eight hours and more during which time the battery was being recharged.
Many battery powered devices in use are extremely energy intensive, such as portable communication transceivers which expend considerable amounts of power during the receive function and more particularly during the transmit function. In order to avoid lengthy recharging times, "rapid" chargers were developed to rapidly recharge the batteries at high charging rates for relatively short time periods, such as from one to three hours, as compared to eight hours or overnight for "trickle" charges.
In order to safely "rapid" charge batteries, numerous problems had to be overcome. Overcharging was the most serious problem which resulted in overheating of the battery. Such heating lead to potential damage to the battery case seals, rupturing of the battery case, and in extreme instances explosive rupturing of the battery case. Prior art "rapid" battery chargers overcame most of these problems by monitoring various battery parameters, such as the terminal voltage and internal cell temperatures. Other "rapid" battery chargers utilized timed charging of the battery to avoid overcharging. Such techniques however, did not necessarily insure the rechargeable battery was not being overcharged in all instances. Since many batteries were not fully discharged at the time the batteries were placed into the charger, the use of such charging techniques as timed charging would overcharge the battery unless the battery was first fully discharged. A number of chargers consequently provided automatic discharge of the batteries for a period of time sufficient to insure a fully charged battery was completely discharged. As a result, the time required to "rapid" charge such batteries was increased due to the time added to first discharge the batteries. There is a need for a controller for a charger which can efficiently control the replenishment of only the energy expended.